The present invention relates to a novel mesomorphic compound, a liquid crystal composition containing the mesomorphic compound adapted for use in liquid optical devices such as display devices and optical shutters.
Chemical compounds having an optically active group have called attention for use as mesomorphic compounds. Chemical compounds characterized by optically active groups have been known to have such functions or usages as follows (i) guest-host electrooptical effect of the White-Taylor type utilizing a chiral nematic phase in a liquid crystal state; (ii) phase transition in an electric field from chiral nematic phase into nematic phase; (iii) phase transition between chiral nematic phase and smectic phase due to heat, (iv) ferroelectricity of smectic phase; (v) a non-linear optical element when formed into a film formed by accumulation of single molecules; and (vi) circular polarization beam-splitter or filter when fixed in a matrix. Therefore, extensive research has been made in order to find chemical compounds adapted for various usages as mentioned above by synthesizing various compounds having chemically active groups and examining their functions.
On the other hand, in the field of liquid crystal devices, there has been a well known type of liquid crystal devices using TN (twisted nematic) type liquid crystals as shown, for example, in "Voltage-Dependent Optical Activity of a Twisted Nematic Liquid Crystal" by M. Schadt and W. Helfrich, Applied Physics Letters Vol. 18, No. 4 (Feb. 15, 1971) pp. 127-128. In this type of liquid crystal devices, the number of picture elements have been restricted, because there is a problem that a crosstalk phenomenon occurs when a device of a matrix electrode structure with a high density of picture elements is driven according to a time-sharing or time-division driving scheme.
As another type of liquid crystal device, there has been known one comprising a plurality of picture elements each connected to and subject to switching by a thin film transistor as a switching element. This type of liquid crystal device, however, is accompanied with problems such that production of thin film transistors on a substrate is very complicated, and production of a display device with a large picture area or screen is difficult.
In order to obviate the above-mentioned drawbacks of the conventional types of liquid crystal devices, Clark and Lagerwall have proposed the use of a liquid crystal device using a bistable liquid crystal (Japanese Laid-Open Patent Application No. 107216/1981, U.S. Pat. No. 4367924, etc.). The bistable liquid crystal to be used may be a ferroelectric liquid crystal having a chiral smectic C (SmC*) phase, chiral smectic H (SmH*) phase, chiral smectic F (SmF*) phase, chiral smectic I (SmI*) phase or chiral smectic G (SmG*) phase.
Such a ferroelectric liquid crystal has bistability, i.e., has two stable states comprising a first stable state and a second stable state. Accordingly, different from the conventional TN-type liquid crystal in the above-mentioned device, the liquid crystal is oriented to the first stable state in response to one electric field vector and to the second stable state in response to the other electric field vector. Further, this type of liquid crystal very quickly assumes either one of the above-mentioned two stable states in reply to an electric field applied thereto and retains the state in the absence of an electric field. By utilizing these properties, essential improvements can be attained with respect to the above-mentioned difficulties involved in the conventional TN-type liquid crystal device.
For such bistable ferroelectric liquid crystal devices, there have hitherto been used such compounds as p-decyloxybenzylidene-p'-amino-2-methylbutyl cinnamate (DOBAMBC), p-hexyloxybenzylidene-p'-amino-2-chloropropyl cinnamate (HOBACPC) and 4-o-(2-methyl)-butylresorcylidene-4'-octylaniline (MBRA 8). However, these compounds are liable to be degraded when repeatedly subjected to application of electric field and therefore require that great care should be excercised in respect of tightness of sealing of cells, sealing conditions and driving conditions, thus providing a serious obstacle to development of the liquid crystal device. On the other hand, research has been made to find stable liquid crystal or mesomorphic compounds, whereas no practical compounds satisfying high response speed and stability have been found.